What is Circuit Breaker Design Pattern in Microservices? How to implement it?

Hello guys, Microservices design patterns are very important concepts for Java developers to learn, not just to create a robust, scalable, and high-performance Microservice architecture but also to do well on Java developer interviews. In the past, I have shared several Microservices design patterns like e Event Sourcing, SAGA, Database Per Microservices, CQRS, API Gateway, and also shared best practices to design Microservices and in this article, I am going to talk about Circuit-Breaker Design Pattern, and how you can implement in Java using Spring Cloud Framework.  This is not just an important Microservice Pattern but also a popular Microservice question which I have also mentioned earlier in my article about 15 Microservices questions for Interviews. If you haven't read that article yet, I suggest read it, especially if you are preparing for Java and Microservice interviews. 


What is Circuit Breaker Design Pattern in Microservices? How to implement it?

In the world of microservices architecture, fault tolerance and resiliency are two of the most important factors to consider. The Circuit Breaker design pattern is an essential tool to achieve this goal. In this article, we will explore what the Circuit Breaker pattern is, how it works, and how to implement it in microservices.

What is Circuit Breaker Design Pattern?

The Circuit Breaker pattern is a design pattern used in software engineering to handle failures in distributed systems. It is used to detect and handle faults in communication between services, preventing them from cascading and causing further damage.

The Circuit Breaker pattern works by wrapping a potentially dangerous or faulty operation in a circuit breaker object. The circuit breaker is designed to detect when the operation is failing or taking too long to complete. 

Once a threshold is reached, the circuit breaker will “trip” and stop the operation from executing, returning a pre-configured fallback value instead. This helps prevent further damage by stopping the faulty operation from cascading through the system.

What is Circuit Breaker Design Pattern?



What is Circuit Breaker Design Pattern in Microservices? How to implement it?

The Circuit Breaker pattern has three states: Closed, Open, and Half-Open.
  • Closed
    In the closed state, the circuit breaker allows requests to flow through and execute the operation as normal.

  • Open
    In the open state, the circuit breaker returns a pre-configured fallback value instead of executing the operation.

  • Half-Open
    In the half-open state, the circuit breaker allows a limited number of requests to pass through to test if the operation is functioning correctly. If these requests succeed, the circuit breaker returns to the closed state. If they fail, the circuit breaker returns to the open state.




How to implement Circuit Breaker Design Pattern in Microservices?

There are several frameworks and libraries available to implement the Circuit Breaker pattern in microservices. In this section, we will explore how to implement the Circuit Breaker pattern using Netflix Hystrix, a widely used library for Circuit Breaker implementation in microservices.

Step 1: Add Hystrix Dependency

The first step is to add the Hystrix dependency to your microservice project. You can add the following dependency to your pom.xml file if you are using Maven:

<dependency>
    <groupId>com.netflix.hystrix</groupId>
    <artifactId>hystrix-core</artifactId>
    <version>1.5.18</version>
</dependency>


Step 2: Create a Hystrix Command

Next, you need to create a Hystrix command that represents the operation you want to execute. You can do this by extending the HystrixCommand class and overriding the run() method with your logic. The run() method should return the result of the operation.

Here’s an example of a Hystrix command that executes an HTTP request using the Apache HttpClient library:

public class HttpCommand extends HystrixCommand<String> {

    private final HttpClient httpClient;
    private final HttpUriRequest request;

    public HttpCommand(HttpClient httpClient, HttpUriRequest request) {
        super(HystrixCommandGroupKey.Factory.asKey("HttpGroup"));
        this.httpClient = httpClient;
        this.request = request;
    }

    @Override
    protected String run() throws Exception {
        HttpResponse response = httpClient.execute(request);
        String result = EntityUtils.toString(response.getEntity());
        return result;
    }
}


Step 3: Configure Hystrix Circuit Breaker

Next, you need to configure the Hystrix circuit breaker for your Hystrix command. You can do this by creating a HystrixCommandProperties object and setting the relevant properties.

Here’s an example of configuring the Hystrix circuit breaker with the following properties:

HystrixCommandProperties.Setter()
        .withCircuitBreakerErrorThresholdPercentage(50)
        .withCircuitBreakerRequestVolumeThreshold(10)
        .withCircuitBreakerSleepWindowInMilliseconds(5000)
        .withExecutionTimeoutEnabled(false));


Step 4: Execute the Hystrix Command

Finally, you can execute the Hystrix command by creating an instance of the command and calling the execute() method. This method will return the result of the operation if it succeeds, or the fallback value if the circuit breaker is open.

Here’s an example of executing the HttpCommand:

HttpClient httpClient = HttpClients.createDefault();
HttpGet request = new HttpGet("https://jsonplaceholder.typicode.com/posts/1");
HttpCommand command = new HttpCommand(httpClient, request);

String result = command.execute();

And, here is a nice sequence diagram which explains how circuit-breaker pattern works in Microservices architecture:


What is Circuit Breaker Design Pattern in Microservices? How to implement it?


Benefits of Using Circuit Breaker Design Pattern

Implementing the Circuit Breaker design pattern in your microservices architecture can provide several benefits, such as:
  1. Fault tolerance
    The Circuit Breaker pattern helps prevent faults from cascading and causing further damage in distributed systems.

  2. Resiliency
    The pattern allows the system to continue functioning, even if one or more services are down or experiencing issues.

  3. Improved performance
    The pattern reduces the amount of time spent waiting for slow or faulty operations to complete, improving overall system performance.

  4. Reduced downtime
    By handling faults in a more efficient and timely manner, the Circuit Breaker pattern can reduce system downtime and improve availability.

  5. Better user experience
    The pattern can help ensure that users have a seamless experience, even when some parts of the system are not functioning correctly.

Best Practices for Implementing Circuit Breaker Design Pattern

When implementing the Circuit Breaker pattern in microservices, there are several best practices that you should follow to ensure the pattern is implemented correctly. These include:

1. Monitoring
It is essential to monitor the performance of the system and the Circuit Breaker pattern itself to ensure it is functioning correctly.

2. Configuring thresholds
The thresholds for when the Circuit Breaker should trip and when it should return to a closed state should be set appropriately, based on the system's specific requirements.

3. Fallback mechanisms
The fallback mechanisms should be carefully designed to ensure they provide meaningful and accurate information to users.

4. Testing
The Circuit Breaker pattern should be thoroughly tested in a variety of scenarios to ensure it is working as intended.

5. Circuit Breaker libraries
Using a well-established and reliable Circuit Breaker library, like Netflix Hystrix, can simplify the implementation process and reduce the likelihood of errors.




Conclusion

The Circuit Breaker design pattern is an essential tool in the world of microservices architecture. It helps handle failures in distributed systems, preventing them from cascading and causing further damage. Implementing the Circuit Breaker pattern using frameworks like Netflix Hystrix is relatively simple and can provide significant benefits to your microservices architecture. 

By following the steps outlined in this article, you can easily implement the Circuit Breaker pattern in your microservices and improve the fault tolerance and resiliency of your system.

Other Java Microservices articles and tutorials you may like:


Thanks for reading this article so far. If you like this Circuit Breaker Microservice design pattern tutorial and when and how to use it then please share them with your friends and colleagues. If you have any questions, feedback, or other fee courses to add to this list, please feel free to suggest.

P. S. - If you are new to Microservice architecture and want to learn more about Microservice Architecture and solutions from scratch and looking for free resources then I highly recommend you to check out my post about 7 free Microservice courses. It contains free Udemy and Coursera and courses to learn Microservice architecture from scratch.  

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